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Tuesday, September 30, 2008

The Volcanism on Io article on Wikipedia has been going through a peer review for the last couple of weeks. Additional comments for the peer review and edits to improve the article are useful. In particular, the article's lead section is need of expansion to fit the overall length of the article.

Feel free to improve the article, even if it is just for grammar. Let's see if we can't get two Io-related articles to Featured Article status.

Wednesday, September 24, 2008

On Monday, I received my copy of the book Volcanism on Io: A Comparison with Earth by JPL researcher Ashley Davies. This book, by Cambridge University Press, was published late last year. I had considered picking up a copy since it was published, but the cost of the book ($133 on Amazon.com) was a significant barrier. Thankfully due to some lowered expenses this month, I was able to pull the trigger on buying this book.

Volcanism on Io is a review of our current knowledge, post-Galileo, of Io's volcanic activity. This is a much more focused publication compared to the other major post-Galileo Io book, Io After Galileo, edited by Rosaly Lopes and John Spencer with chapters contributed by nearly 30 authors, including yours truly. The book focuses on modeling of volcanic activity, particularly how thermal emission observed from remote instruments can be related to the style of volcanic activity. Davies also spends several chapters on reviewing our current ideas for the eruption styles at several distinct volcanoes, including Loki, Pele, Tvashtar, Prometheus, Amirani, and Pillan.

The meat of the book comes from Davies's explanation of his lava cooling model, presenting step-by-step the various aspects of it including the equations he uses. I wish more diagrams were used to show how some of the variables he uses inter-relate, making some parts of his explanation a bit hard to follow. Also, the chapter in question, Models of Effusive Eruption Processes, is largely a rewrite of the author's 2005 paper on the subject. This fact highlights my most important criticism of this book. Davies does a great job in covering the subjects that are in his wheelhouse: NIMS observations of Io's volcanic activity, internal structure, and modeling of terrestrial and ionian volcanism. Discussion of subjects that are less so, like volcanic plumes and geomorphology, seem to rushed. For example, I would have loved to have seen a chapter covering modeling of volcanic plumes in as much detail as the one on effusive eruption modeling.

Volcanism on Io, with the exception of parts of Chapter 7 where more illustrations could have been very helpful in understanding the equations he was presenting, the book is well illustrated, presenting models based on our current understanding of Ionian volcanism. This is particularly useful in his cutaway views showing the envisioned structure of Io's lithosphere in Chapter 18 and of paterae formation in Chapter 15.

Volcanism on Io provides a focused examination of several of Io's volcanoes. Applying the models Davies presented in the preceding chapters, the author provides in this book a detailed analysis of the eruption styles of specific volcanic centers. I almost wished he expanded his analysis to more volcanoes, like Isum (where several eruptions centered on Io's largest fissure were observed by Galileo), Hi'iaka (a patera with a potentially unique formation process), Kanehekili, and Masubi. It should be noted that the manuscript was likely written sometime in late 2006, before the New Horizons flyby as no results from that encounter are presented.

Ashley Davies's Volcanism on Io is an in-depth look at an important aspect of Ionian science, its volcanic activity. The book provides a review of our current state of knowledge in the subject and focuses on Davies's own models for how the observed thermal emission relate to several important eruption parameters, such as volumetric flow rate, and further, how those relate to eruption style. Davies does an excellent job in explaining how these different eruption styles work. I wish Davies had spent more time on subjects that are not in his wheel house, such as the geomorphology of volcanic terrains and volcanic plumes. Still, I definitely recommend this book for people wanting to better understand the nitty-gritty of perhaps the most important aspect of Io science, the active volcanism on display.

Monday, September 22, 2008

Well I finally pulled the trigger on this book and ordered it on Amazon last week. Volcanism on Io: A Comparison with Earth by Ashley Davies is a comprehensive overview of the current state of knowledge into the volcanism displayed on the surface of Io. An overview of terrestrial volcanism and remote sensing studies is provided as a background to better understand what we see on Io.

The book arrived via UPS this morning and am slowly working my way through the book. I plan on providing a thorough review sometime this week on this impressive tome.

Sunday, September 21, 2008

A fresh eruption at Reunion Island's Piton de la Fournaise volcano today produced a new basaltic lava and a large lava pond and an increase in SO2 concentration within its eight kilometer-wide caldera. Thomas Staudacher, from the volcano observatory on Reunion captured the view at left of the caldera showing this fresh flow. While this eruption seems pretty minor, Piton de la Fournaise (or Le Volcan to the local residents) has recently seen an uptick in activity. According to the AFP, an eruption in April 2007 resulted in the partial collapse of the volcano's caldera and included vigorous fire fountaining that reached upwards of 200 meters into the air.

The last major paper on Io out of the Galileo mission was published in the October 2008 issue of the journal Icarus. "Galileo observations of volcanic plumes on Io," by USGS researcher Paul Geissler and NAU grad student Melissa McMillan, describes the observations acquired of Io's plumes during the entire Galileo mission. The abstract can be found at the link above, but the article itself is available to subscribers (individual or institution) only.

In this paper, the authors searched the Galileo SSI data set for volcanic plumes on Io, then used those images to determine particle sizes, column densities, and plume masses.

In all, the authors found plumes at 13 sites spread out across Io. These include optically bright dust plumes (like the one shown at left), faint dust plumes, and gas plumes, with the latter seen in eclipse observations by Galileo. In some cases, the authors found several of these types at a single volcanic center. For example, on I31 in August 2001, a Prometheus-type dust plume was observed at Thor, which was vigorously erupting at the time. A faint outer halo was also observed in the high phase angle images from that orbit. Pele-type plumes, large, faint plumes generated from gas emitted from lava fountains, went largely unseen by Galileo as SSI had poor sensitivity in the ultraviolet where these types of plumes are best seen. Pele's plume was observed on two occasions, during E4 and G29. Another Pele-type plume was also observed at Grian, resulting in a transient large plume deposit. Several Pele-type deposits were also observed, at Dazhbog and Tvashtar, while additional changes at Pele suggest that additional large plumes existed during the Galileo mission.

The authors then examined the visible-light spectrum of various dust plumes to determine the mean particle size and total plume mass. The authors determined that the small, optically-dense plumes seen at such volcanoes as Zamama, Pillan, and Prometheus consist of course-grained "ash" particles. Combined with the presence of a central dense column in these plumes, and the authors suggest that these particles erupt with the gas in the plume. Typical mass for these plumes was found to be around 106 to 107 kg. The authors also examined the faint outer halo at Thor. They found that the faintness of the plume is not because there is very little dust, but because they are made of much finer particles, 10 nm versus the 80-120 nm found in the brighter core of the plume. With particles that small, the plume would be more easily visible at ultraviolet wavelengths. Strangely enough, the faint outer halo has 10-100 times more mass than the inner, "dense" core. Keep in mind, as well, that even accounting for that inner core, the dust makes up only 10% of mass of these plumes, with the gas making up for the rest of it. The particles in the faint outer halo at Thor (and seen at Loki during the Voyager 1 flyby) are thought to condense directly from the gas in the plume, forming small, sulfur "snowflakes."

The authors also compared the observed plumes to the surface changes found by Galileo. They determined that the surfaces changes were caused by the dense, dust plumes, and not by the fainter gas/snowflake plumes, except in the case of the Pele-type plumes, which produce large, red rings. The deposits made by the gas plumes likely take the form of SO2 frost that is transparent at visible wavelengths. The mass of the plumes suggests that dust fallout makes up only a small fraction of the overall resurfacing on Io.

The table of contents for the October 2008 issue of Icarus is now online. Included in this issue is "Galileo observations of volcanic plumes on Io" by Paul Geissler and Michelle McMillan. Geissler and McMillan describe the observations of Io's volcanic plumes as observed by Galileo, and look into the differences in appearance between the gas plumes observed in eclipse and the dust component observed in daylight. The paper was posted online in about four months, and yes, I still intend on doing a full post on that paper.

Tuesday, September 16, 2008

The abstracts for next month's Division of Planetary Sciences Meeting are now online. Several talks and posters are about everyone's favorite moon. The abstracts for DPS (and the upcoming AGU meeting in December) are much shorter than those submitted for LPSC, which would be better described as mini-papers. So there is less to say about the abstracts themselves. A few abstracts do stand out:

Julie Rathbun and John Spencer have a talk scheduled for the morning of October 15 titled, "Io Eclipse Observations: Determining the History of Loki’s Flux at Multiple Wavelengths." The abstract just summarizes Loki's importance to Io's total heat flux and Rathbun and Spencer's theory for Loki's observed activity. The talk will cover their work on separating Loki's contribution to the observed heat flux from the other volcanoes on the sub-Jovian hemisphere. They will then discuss Loki's extracted brightness at three wavelengths in the near-infrared.

Erinna Chen et al. will present a poster covering her group's summer school Team X project, a New Frontiers-class Io mission concept. The mission, which they call Argus, would use a high-inclination orbit around Jupiter and would flyby Io at least 40 times. The mission would use Advanced Stirling Radioisotope Generators (ASRG) as a power source, pushing the mission to after Discovery 2013. The payload included in the study would consist of a narrow-angle camera, a thermal imager, an NIR spectrometer, a UV spectrometer, and an INMS-like instrument, similar to the IVO Discovery mission concept, but with more advanced instrumentation and 4-10 times the number of Io flybys, so presumably the increased cost between the Discovery mission concept and this New Frontiers mission would be taken up in increased payload size and radiation shielding.

While I will not be at the conference, I am a co-author on three abstracts: "Evidence for Past Lake-Level Change in Titan's Ontario Lacus" by Jason Barnes et al., "Tiger Stripes and Cassini ISS High-Resolution Imaging of Enceladus" by Paul Helfenstein et al., and "Cassini Imaging Observations of Titan’s High-Latitude Lakes" by Elizabeth Turtle et al. Of these, I spent the most time working on the last one, and includes the coolest discovery we have made at Titan from Cassini images:

Differences between the two ISS observations may be due to changes on the surface as a result of precipitation from a large cloud system observed in Fall 2004 (Schaller et al., 2006), although diffuse clouds or atmospheric scattering could also play a role.

The meeting will occur between October 10-15 in Ithaca, New York on the Cornell University campus.

I am sorry for my long absence here on this blog. I am sure many of you are wondering what has been going on with Io lately so I thought I would finally give this blog a big of a kick-start. Rather than post long posts covering what has happened since May, I thought I would just provide a quick summary:

NASA has pushed the downselection of the next Outer Planets Flagship Mission to February 2009 from this November. This will provide an opportunity for the community to digest the mission studies due from the two teams on November 3. In June, NASA removed the $2.1 billion cost cap in favor of a "sweet spot" strategy, allowing the study teams to determine a price that would provide the best science per dollar. This has increased the cost of both missions to around $3 billion.

With respect to Io, "sweet spot" science for the Jupiter Europa Orbiter would include 3-5 Io flybys during a 24-33 month long Jupiter orbital phase. According to the above presentation, these missions would provide the first direct sampling of Io's volcanic plumes, which would indicate that they would try to target one, presumably Pele or Tvashtar. However, the "sweet spot" mission would not include a dust detector or an INMS-like instrument, which would provide crucial information on this regard. It would include a particle instrument, however.

The next Outer Planet Assessment Group (OPAG) meeting will take place November 6-7 in Tempe, Arizona. Obviously, the Flagship missions will be an important part of the discussion, along with the Discovery & Scout Mission Capability Expansion program.

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I work for the Cassini Imaging team, usually processing Titan and Enceladus images and making maps of Titan based on our images. When I am not working or studying, I'm...I forget. I watch a lot of movies I guess.